This invention relates to a photographic film cassette, and more particularly to a photographic film cassette in which a leader end of a photographic film strip is advanced outwardly from the interior of the cassette when a spool is unwound.
In single lens reflex (SLR) cameras and in compact cameras, a 135 type photographic film cassette is most commonly used. This 135 type film cassette includes a cylindrical cassette body having a film passage mouth, a spool rotatably supported within this cassette body, and a 35 mm wide photographic film strip roll (hereinafter referred to as the "film") coiled on the spool. A film leader section of the film protrudes from the film passage mouth. The film leader section is pulled out slightly from the cassette because, when a film cassette is loaded in a film supply chamber of a camera, a sprocket, disposed between the film supply chamber and a film take-up chamber and adapted initially to feed the film, is brought into engagement with a perforation formed in the film leader section, so that the film leader section can be sent reliably into the film takeup chamber in accordance with rotation of this sprocket.
Recently, a film cassette has been proposed in which, when a spool is unwound, a film roll coiled on the spool is rotated together with the spool to advance the film leader end of the film roll outwardly from the interior of the cassette, and supply the film to the film take-up chamber. In this film cassette, no initial feeder mechanism, including the sprocket mentioned above, is required. Moreover, since the film leader section is held within the cassette, the cassette has the advantage of being easy to handle.
However, this film cassette has such shortcomings that when the film roll is rotated because of vibration during transportation, the film leader end may protrude accidentally from the film passage mouth, or otherwise may be drawn back fully into the cassette beyond the film passage mouth. When the film leader end protrudes from the cassette, this film cassette has no specific feature. On the other hand, when the film leader end is drawn back into the cassette beyond the film passage mouth, it sometimes happens that the film leader end cannot be advanced, even if the spool is unwound.
When the film cassette is being used, it is loaded in the camera and pulled out from the cassette, one frame at a time, and a picture is taken in each frame. After all the frames have been exposed to take pictures, the spool is wound to coil the exposed film onto the spool. The exposed or used film cassette is removed from the camera and is taken to a photofinishing laboratory. If the spool should, for some reason or other, be unwound before it is submitted to the laboratory, the exposed film would be advanced outside the cassette. Therefore, this conventional film cassette is not safe.
If the film leader end is drawn back fully into the cassette beyond the film passage mouth when the exposed film is wound on the spool, it sometimes happens that the film leader end is not advanced from the cassette even if the spool is unwound when the film is to be processed. In such a case, the cassette must be disassembled in order to remove the film from the cassette. Furthermore, there is another problem in that, when the film roll is wound loosely on the spool, unwinding of the spool is not transmitted smoothly to the film leader section, and reliable advancement of the film is difficult to obtain.
In the film cassette of the type which advances the film by rotating the spool, the film leader section does not protrude from the cassette before or after exposure or use of the film. Therefore, it is practically impossible to tell the difference between a new film cassette (or unused film cassette) and an exposed film cassette (or used film cassette) from the appearance of the film cassette. As a consequence, there is a risk that an exposed film cassette will be reloaded in a camera by mistake.